digest 0.4.0 and 0.4.1

After almost two years, I just made a small update to thedigest
package for R by adding sha-256 as another supported hashing function.
While at this, a few minor edits where made here or there. Version 0.4.0
also included a file src/Makefile.win but as that actually prevents
a successful build on the Windows platform I promptly removed it for a
(more-or-less brown-bag) release 0.4.1. Thanks to Uwe Ligges and his
automated win-builder service
that permits easy unattended build tests on that platform.